A decrease in the cardiac contractility has been linked to a fall in the intracellular pH and to changes in the electrolyte composition of the intracellular fluid of the heart. In the proposed study, the internal environment of the cardiac ventricle will be monitored during chronic metabolic acidosis and changes in the composition of the intracellular fluid of the heart will be related to the whole-body buffering reactions which occur during the acidosis. Rats will be subjected to prolonged non-carbonic acidosis by the continued administration of ammonium chloride in their diet. The intracellular fluid of the heart will be analyzed at various times during the acidosis. Changes in the internal composition of the cardiac ventricle will be related to the time course of renal, extracellular, muscular and skeletal buffering during the acidosis. These neutralization reactions will be characterized by the repeated, direct analysis of the acid content of the urine and the buffer content of the extracellular fluid, skeletal muscle and bone. The effect of the magnitude of the acid load on these dynamic relationships will be explored along with the effect of the rate at which the acid load is imposed. The acid-base state and electrolyte composition of the intracellular fluid of the heart, the rate of acid excretion by the kidneys and the dynamic response of the buffer stores of the extracellular fluid, skeletal muscle, and bone will also be analyzed during recovery from the acidosis or the acute worsening of the chronic acidosis.